Understand Einstein's theory of relativity

Sometimes the easiest way to understand a concept is to think of a phrase to sum it up.

The apathy of matter is the death of energy. The limit of energy is the accumulation of matter. Between these two limits every state of matter is relative.

I’ve got the special theory pretty much down, conceptually. I came across some audio lectures which have been very good. But special relativity is the easy part. It’s all very well considering objects in uniform motion… but I’m now onto general relativity, and the gravitational theory of 4-dimensional spacetime. Which kind of breaks my brain every time I think about it.